84 
IOWA ACADEMY OF SCIENCE Voi,. XXVIII, 1921 
Shaw used his instrument only for measuring the displacement of 
the diaphragm of a telephone receiver. In this work the instrument 
was used to measure the amplitude of vibration of the diaphragm 
when it was excited by an alternating current. 
Measurements were not made directly on the tone generator be- 
cause its position of equilibrium did not remain fixed. The ampli- 
tude of vibration of the diaphragm of an ordinary head receiver 
was measured and then by a method of comparison the desired 
measurements were obtained. From data on the receiver, curves 
were plotted which showed the relation between the amplitude of 
the receiver diaphragm and the current through it. Figure 10 
Fig. 10 
shows one of the curves for a frequency of 1200 vibrations per 
second. All of the curves obtained were similar to this, showing 
an approximate linear relation between the current and the ampli- 
tude. In Table 1 below are some of the constants which when 
TABLE I 
Frequency Constant 
(Amplitude for 1 Ampere) 
1200 .075 cm. 
1440 .0235 cm. 
1600 .0175 cm. 
2200 .0070 cm. 
3700 .0412 cm. 
